Six years of unexplained delay moves the burden

How to read the ledger below. Each numbered point carries the kind of evidence behind it. ESTABLISHED is stated in the authority's own text, with a locator. IMPLEMENTED is the rule as the authority actually applied it. OBSERVED is carried by a source outside this one. ASSUMED is the drafter's inference, flagged as such and not the authority speaking. Quotations are checked against a cached copy of the primary source by script.

In one paragraph

The Federal Circuit held in Hyatt v. Hirshfeld on 1 June 2021 that prosecution laches requires both unreasonable and inexcusable delay under the totality of the circumstances and prejudice attributable to that delay, that prejudice means intervening rights in the sense that someone invested in or worked on or used the claimed technology during the delay, and that where the Patent Office shows unreasonable and unexplained delay exceeding 6 years the burden shifts to the applicant to prove the absence of prejudice. The court vacated and remanded so the applicant could be heard on the issue the shift had made his to address.

Reader summary

This is the case the modern prosecution-laches doctrine runs through. The Patent Office asserted laches as an affirmative defence in a district-court action, lost at trial on the ground that it had not carried its burden, and appealed.

The Federal Circuit set out the test in two elements: unreasonable and inexcusable delay under the totality of the circumstances, and prejudice attributable to that delay. It defined prejudice concretely, as intervening rights, meaning that the accused infringer or others invested in, worked on, or used the claimed technology during the period of delay.

Then it did the thing that makes this record load-bearing. Where the Office demonstrated unreasonable and unexplained delay exceeding six years by any measure, that showing shifts the burden to the applicant to prove lack of prejudice. The court nonetheless vacated and remanded rather than deciding the point against the applicant, so that he could present evidence on an issue the shift had newly made his to address, and it retained jurisdiction over the remaining invalidity questions.

The six-year figure is the part most likely to be misremembered. It is not a statutory period and not a safe harbour. It is a description of the delay actually before the court, used to justify shifting a burden, and the pair records in this tier show the doctrine turning on evidence rather than on elapsed time.

Why this matters when you are drafting

Know which side of the burden you are on. Claim 3 is the practical core. Prejudice is ordinarily the challenger's to prove, and past a large unexplained delay it becomes the applicant's to disprove. That is a different litigation posture and it is worth knowing before a family gets long.

"Unexplained" is doing as much work as "unreasonable." Claim 3 pairs the two. A long pendency with a documented, ordinary explanation is a materially different record from one without. What the file history shows about why prosecution took the shape it did is therefore part of the asset.

Prejudice has a concrete test you can assess. Claim 2. Ask whether anyone invested in, worked on, or used the claimed technology during the delay. That is a factual question about the market, answerable before assertion rather than after.

Do not carry away "six years." Claim 9. It describes the delay in this case, not a period after which laches attaches or before which it does not. google-v-sonos in this tier is the case where a district court's reliance on the magnitude of delay was reversed.

Laches can be dispositive of everything. Claim 5: the court treated it as potentially resolving the entire case and sequenced around it. It is not a secondary defence.

What the authority establishes

[ESTABLISHED, the two-element test the whole tier uses] A party must show "that the patentee's delay in prosecution was unreasonable and inexcusable under the totality of circumstances, and (b) that the accused infringer suffered prejudice attributable to the delay". (P. 23.)

[ESTABLISHED, what prejudice means, and it is concrete] "To establish prejudice, we explained, an accused infringer must show evidence of intervening rights, that is, that the accused infringer or others 'invested in, worked on, or used the claimed technology during the period of delay.'" (P. 23.)

[ESTABLISHED, the burden-shifting holding] "we conclude that the PTO's demonstration of an unreasonable and unexplained delay by Hyatt, which exceeds six years by any measure, shifts the burden to Hyatt to prove lack of prejudice". (P. 38.)

[ESTABLISHED, the disposition, and it is not a win for the Office] "consistent with the principles of fairness and due process, we vacate and remand the district court's decision on prosecution laches for further proceedings consistent with this opinion and to provide Hyatt the opportunity to present evidence on that issue". (P. 2.)

[ESTABLISHED, jurisdiction retained] "[g]iven the potential for the prosecution laches issue to resolve the entire case at hand, we retain jurisdiction over the appeal with respect to the anticipation and written description issues, and we remand to the district court for the limited purpose of affording Hyatt the opportunity" to be heard. (P. 40.) Laches was treated as potentially case-dispositive.

[ESTABLISHED, the procedural posture] "The Patent and Trademark Office asserted affirmative defenses of prosecution laches and invalidity for anticipation and lack of written description." (P. 2.) "The district court first held a trial on prosecution laches and subsequently held trials on anticipation and written description." (P. 2.)

[ESTABLISHED, what happened below] "Following a Rule 52(c) motion at the first trial, the district court decided that the Patent and Trademark Office failed to carry its burden of proving prosecution laches." (P. 2.) The appeal is from that failure.

[ESTABLISHED, the applicant's grounds, which map the ways the defence can fail] Hyatt argued the Office "did not prove intervening rights; (iii) never issued laches rejections for the four applications at issue; and (iv) failed to meet its burden of proving unreasonable and unexplained delay by a preponderance of the evidence". (P. 15.)

[IMPLEMENTED, the shift is a consequence of scale, not a rule keyed to a number] Claim 3 ties the shift to delay "which exceeds six years by any measure" on these facts. The court does not announce six years as a threshold; it uses the magnitude of an established delay to justify reallocating a burden.

[ASSUMED, drafter's inference, flagged as such] Claims 2 and 3 together explain why the pair records diverge. Prejudice defined as intervening investment is provable from an accused product's development history, so where a defendant built during the delay the element is comparatively easy; where it did not, the defence fails even on a long family. The opinion does not draw that connection to later cases, which postdate it.

Quotations, verified against the source

All from the Federal Circuit's opinion. Page locators computed from the docket stamp.

"consistent with the principles of fairness and due process, we vacate and remand the district court's decision on prosecution laches for further proceedings consistent with this opinion and to provide Hyatt the opportunity to present evidence on that issue" (P. 2.)
"The Patent and Trademark Office asserted affirmative defenses of prosecution laches and invalidity for anticipation and lack of written description." (P. 2.)
"The district court first held a trial on prosecution laches and subsequently held trials on anticipation and written description." (P. 2.)
"Following a Rule 52(c) motion at the first trial, the district court decided that the Patent and Trademark Office failed to carry its burden of proving prosecution laches." (P. 2.)
"did not prove intervening rights; (iii) never issued laches rejections for the four applications at issue; and (iv) failed to meet its burden of proving unreasonable and unexplained delay by a preponderance of the evidence" (P. 15.)
"that the patentee's delay in prosecution was unreasonable and inexcusable under the totality of circumstances, and (b) that the accused infringer suffered prejudice attributable to the delay" (P. 23.)
"To establish prejudice, we explained, an accused infringer must show evidence of intervening rights, that is, that the accused infringer or others 'invested in, worked on, or used the claimed technology during the period of delay.'" (P. 23.)
"we conclude that the PTO's demonstration of an unreasonable and unexplained delay by Hyatt, which exceeds six years by any measure, shifts the burden to Hyatt to prove lack of prejudice" (P. 38.)

Tensions and open questions

The six-year figure invites exactly the misreading claim 9 warns against. It is stated as a description of this delay and is the most quotable number in the doctrine, so it will be carried as a threshold whether or not it is one.

What discharges the shifted burden is not specified. Claim 3 moves the burden and claim 4 remands so it can be addressed, without saying what evidence of no prejudice would look like.

The defence here was asserted by the Office, not by an accused infringer. Claims 1 and 2 are phrased in terms of an accused infringer, while the party asserting laches was the Patent Office. How the intervening-rights test operates for a party that is not an accused infringer is not squarely addressed in the passages read.

Unresolved by this record: the outcome on remand. The court vacated and retained jurisdiction. Nothing here says how it came out.

What this record does and does not cover

The prosecution-laches analysis was read end to end, including the two-element statement, the definition of prejudice and the burden-shifting holding, because those are what the rest of Tier D depends on.

What was NOT read closely, and is therefore outside what this record can support: the anticipation and written-description issues, and the factual detail of the applicant's prosecution history beyond the characterizations quoted. This record says nothing about whether the claims were valid, and nothing about what happened on remand.

Currency

This record was verified against its primary source on 2026-08-15. That is a fidelity check: the quotations, locators and attribution are accurate to that source. Whether the authority has since been narrowed, distinguished, abrogated or reversed has not been checked here. Confirm it still stands before relying on it.